There are a wide variety of cylindrical containers constructed from different materials and in different configurations to accommodate a wide variety of uses. Notwithstanding such variety, metal containers can be generally categorized as either two-piece or three-piece. Two-piece containers are typically manufactured by a drawing and ironing process to produce a container having a continuous bottom and sidewall to which a separate end piece is connected. Three-piece containers are typically manufactured from metal roll stock that is cut into strips having a width that will substantially define the height of the resultant container and a length which will effectively define its diameter. Each strip is then formed into a cylindrical shape and the opposing edges of the strip are attached by processes known in the art, such as welding. With this type of construction, two end pieces must be separately attached to the cylinder to form a closed container.
Whether construction is achieved by two- or three-piece methods, a key portion of the construction process relates to attachment of at least one end piece to the container. In this regard, a flange is typically formed on the open end(s) of the container to receive an end piece. The flange, which is most often a continuation of the sidewall of the container, is formed to yield the desired angular relationship for mating end piece connection.
One method often used to secure an end piece to a preformed flange is known as curling. An end piece, typically having a hooked outer edge, is placed on the flanged end(s) of the container. After properly positioning the end piece, the flange and the end piece are curled together to form the seal. FIG. 1 illustrates a typical seal formed in this fashion on a typical container with A being the end piece, B being a sidewall, and C being the flange.
Regardless of the method employed to secure an end piece to a container, it is important to have a flange of sufficient width and uniformity in order to achieve an acceptable seal. Due to the manner in which flanges are typically formed, however, such as by using various dies and/or forming rollers, desired tolerances for flange width and uniformity can be difficult to achieve.
Satisfaction of flange width and uniformity requirements can be further hindered when additional container forming processes, such as necking, are performed in the flange region. Necking processes often entail inwardly cold working a container sidewall wherein axial progression is non-synchronous about the periphery of the container. For example, in spin flow forming processes, an outer forming roller is employed to neck and at least partially form a flange on a container sidewall by inwardly working a rotating container in a spiral fashion. As will be appreciated by those skilled in the art, such necking can, depending upon the inward extent thereof, contribute to flange non-uniformities and resultant end-piece sealing difficulties.